Emailable

Emailable (previously known as The Checker) is a good email validation service you can integrate with TexAu.

Try it here: Marketing Automation | TexAu

First, go to the Emailable API page and add a new key:



Give your key a name, set security as "private" key type as "live" and save it:



Finally, input your API key and the email you want to verify in TexAu: